<!DOCTYPE html>
<!--
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　 /　│　　 ／　／
　│　Z ＿,＜　／　　 /`ヽ
　│　　　　　ヽ　　 /　　〉
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　ｲ●　､　●　⊂⊃  〈　　/
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　 ヽ_ﾉ　　(_／　│ ／／
　　7　　　　　　|／
　　＞―r￣￣`ｰ―＿
皮卡丘,对偷看者使用十万伏特
-->
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>canvas background</title>
  <script type="text/javascript" src="jquery.js"></script>
</head>

<body>
  <canvas id="canvas"></canvas>
  <script type="text/javascript">
  function fn() {
    window.requestAnimFrame = (function() {
      return window.requestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        function(callback) {
          window.setTimeout(callback, 1000 / 60);
        }
    })();

    var canvas = document.getElementById('canvas'),
      ctx = canvas.getContext('2d'),
      w = canvas.width = window.innerWidth,
      h = canvas.height = window.innerHeight,
      hue = 200,
      stars = [],
      count = 0,
      maxStars = 1200;

    var canvas2 = document.createElement('canvas'),
      ctx2 = canvas2.getContext('2d');

    canvas2.width = 100;
    canvas2.height = 100;

    var half = canvas2.width / 2,
      gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);

    gradient2.addColorStop(0.025, '#FFFFFF');
    gradient2.addColorStop(1, 'hsl(' + hue + ', 61%, 33%)');
    gradient2.addColorStop(0.15, 'hsl(' + hue + ', 64%, 6%)');
    gradient2.addColorStop(1, 'transparent');
    ctx2.fillStyle = gradient2;
    ctx2.beginPath();
    ctx2.arc(half, half, half, 0, Math.PI * 2);
    ctx2.fill();

    function random(min, max) {
      if (arguments.length < 2) {
        max = min;
        min = 0
      }

      if (min > max) {
        var hold = max;
        max = min;
        min = hold
      }

      return Math.floor(Math.random() * (max - min + 1)) + min;
    }

    function maxOrbit(x, y) {
      var max = Math.max(x, y),
        diameter = Math.round(Math.sqrt(max * max + max * max));

      return diameter / 2;
    }

    var Star = function() {
      this.orbitRadius = random(maxOrbit(w, h));
      this.radius = random(60, this.orbitRadius) / 12;
      this.orbitX = w / 2;
      this.orbitY = h / 2;
      this.timePassed = random(0, maxStars);
      this.speed = random(this.orbitRadius) / 900000;
      this.alpha = random(2, 10) / 10;

      count++;
      stars[count] = this
    };

    Star.prototype.draw = function() {
      var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
        y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
        twinkle = random(10);

      if (twinkle === 1 && this.alpha > 0) {
        this.alpha -= 0.05
      } else if (twinkle === 2 && this.alpha < 1) {
        this.alpha += 0.05
      }

      ctx.globalAlpha = this.alpha;
      ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
      this.timePassed += this.speed
    };

    for (var i = 0; i < maxStars; i++) {
      new Star()
    }

    function animation() {
      ctx.globalCompositeOperation = 'source-over';
      ctx.globalAlpha = 0.8;
      ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)';
      ctx.fillRect(0, 0, w, h);
      ctx.globalCompositeOperation = 'lighter';

      for (var i = 1, l = stars.length; i < l; i++) {
        stars[i].draw()
      };

      window.requestAnimationFrame(animation)
    }

    animation();
  }

  fn();
  </script>
</body>

</html>